Polymer modified bitumen cap sheets and methods

ABSTRACT

According to one embodiment, a method for pressing roofing granules into a roofing membrane may include providing a roofing membrane and applying roofing granules atop a surface of the membrane. The method may also include adjusting a position of a second roller relative to a first roller so as to vary an amount of contact between the membrane and the first roller and pressing the roofing granules into the membrane via the first roller. In some embodiments, a line speed of the membrane may be determined and a contact value may be calculated based on the line speed of the membrane. The contact value may represent an effective amount of contact between the membrane and the first roller. The position of the second roller may be adjusted so that the amount of contact between the membrane and the first roller corresponds to the effective amount of contact.

This patent application is a division of pending U.S. patent applicationSer. No. 13/692,093 filed Dec. 3, 2012.

BACKGROUND OF THE INVENTION

It is often desirable to apply roofing granules to roofing membranes bypressing the granules into a surface of the membranes. The granules aretypically applied for various aesthetics and/or functional purposes,such as to provide ultraviolet (UV) protection and/or foot trafficprotection for the asphalt and underlying membrane. Conventional granuleapplication processes typical involve passing a roofing membrane andgranules through a pair of press rollers to mechanically force thegranules into the roofing membrane. The press rollers are typicallysmall in diameter and apply a single point pressure to the roofingmembrane and granules to force the granules into the roofing membrane.

This conventional process, however, is often less effective at pressinggranules into roofing membranes that exhibit elastic behavior becausethe elastic behavior of such materials often causes the roofing membraneto deflect under the instant point load applied by the press rollersduring the granule pressing process. This deflection may cause theroofing membrane to elastically rebound or return to an originalposition and force the granule out of a temporary pocket that is createdby or during the granule pressing process. The result may be that asubstantial portion of the granules do not properly adhere to theroofing membrane, which may instantly or quickly fall off as minor loadsare applied to the roofing membranes and granules, such as by an objectrubbing against the granules.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the invention describe methods, systems, and apparatus,which improve granule adhesion in roofing membranes. According to oneaspect, a method for pressing roofing granules into athermoplastic-rubber roofing membrane is provided. According to themethod, a thermoplastic rubber material is provided. The thermoplasticrubber material is then heated and extruded to form a membrane having afirst surface and a second surface opposite the first surface. Roofinggranules are then applied atop the first surface, which are to bepressed into the membrane. In relation to pressing the granules, acontact angle is calculated that represents an effective amount ofcontact between the thermoplastic rubber membrane and a press roller.The contact angle may be calculated based on a line speed of thethermoplastic rubber membrane, based on an angular frequency of thepress roller, based on a radius of the press roller, and the like. Thecontact between the thermoplastic rubber membrane and the press rollermay then be adjusted or varied so that the contact corresponds to thecalculated effective amount of contact. According to some embodiments,the contact between the thermoplastic rubber membrane and the pressroller may be adjusted or varied by adjusting a position of a secondroller relative to the press roller. The roofing granules are thenpressed into the first surface of the thermoplastic rubber membrane viathe press roller.

According to another aspect, a method for pressing roofing granules intoa roofing membrane is provided. According to the method, a roofingmembrane is provided. Roofing granules are applied atop a surface of theroofing membrane for subsequent pressing into the roofing membrane. Aposition of a second roller (i.e., positioning roller) relative to afirst roller (i.e., press roller) is adjusted to vary an amount ofcontact between the roofing membrane and the first roller. The roofinggranules are then pressed into the roofing membrane via the firstroller.

In some embodiments, the method may also include the steps of:determining a line speed of the roofing membrane through a granule presssystem, calculating a contact value based on the line speed of theroofing membrane where the contact value represents an effective amountof contact between the roofing membrane and the first roller, andadjusting the position of the second roller so that the amount ofcontact between the roofing membrane and the first roller corresponds tothe effective amount of contact. In some embodiments, the method mayfurther include the steps of: determining an angular frequency of thefirst roller and calculating the contact value based additionally on theangular frequency of the first roller.

According to another aspect, a method for determining a contact anglefor pressing roofing granules into a roofing membrane is provided.According to the method, a radius of a press roller is determined. Thepress roller may be used to press roofing granules into the roofingmembrane. An angular frequency of the press roller is also determined. Aline speed of the roofing membrane through a granule pressing system issimilarly determined and the contact angle is calculated based on theradius of the press roller, the angular frequency of the press roller,and/or the line speed of the roofing membrane. The contact angle definesan amount of contact between the roofing membrane and the press rollerthat effectively press roofing granules into the roofing membrane. Insome embodiments, the angular frequency of the press roller may bedetermined based on a temperature of the roofing membrane.

According to another aspect, a system for pressing granules into aroofing membrane is provided. The system includes a granule applicationdevice that is positionable above a top surface of a roofing membraneand that is configured to dispense roofing granules onto the top surfaceof the roofing membrane. The system also includes a first roller that ispositionable along a path of the roofing membrane through the system andthat is configured to press the roofing granules into the roofingmembrane. The system further includes a second roller that ispositionable along the path of the roofing membrane and that isconfigured to be adjusted relative to the first roller to vary an amountof contact between the roofing membrane and the first roller. Accordingto some embodiments, the second roller may be adjusted based on a linespeed of the roofing membrane through the system, based on an angularfrequency of the first roller, based on a radius or diameter of thefirst roller, and the like.

In some embodiments, the second roller is positioned immediatelyadjacent the first roller along the path of the roofing membrane. Insome embodiments, the second roller is linearly adjustable relative tothe first roller. In some embodiments, the second roller wraps theroofing membrane around at least a portion of the first roller orunwraps the roofing membrane therefrom.

In some embodiments, the first roller has a radius of between about 0.25and 0.75 meters, or of about 0.5 meters. In some embodiments, the secondroller is configured to vary the amount of contact between the roofingmembrane and the first roller by between about 60 and 120 degrees(between 1.04 and 2.09 radians). In other embodiments, the second rolleris configured to vary the amount of contact between the roofing membraneand the first roller by between about 75 and 105 degrees (between 1.30and 1.83 radians). In yet other embodiments, the second roller isconfigured to vary the amount of contact between the roofing membraneand the first roller by between about 85 and 95 degrees (between 1.48and 1.66 radians).

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in conjunction with the appendedfigures:

FIG. 1 illustrates a graph showing a measured pressure applied during agranule pressing operation according to an embodiment of the invention.

FIG. 2 illustrates a graph showing a dynamic mechanical analysis (DMA)frequency-temperature response of a styrene-butadiene-styrene (SBS)modified bitumen roofing membrane according to an embodiment of theinvention.

FIG. 3 illustrates a system designed to press granules into a roofingmembrane with the dwell time of the granule pressure application processincreased according to an embodiment of the invention.

FIG. 4 illustrates the system of FIG. 3 with an adjustable rollerpositioned in front of a press roller so that a membrane passes over theadjustable roller before contacting the press roller according to anembodiment of the invention.

FIG. 5 illustrates a method for pressing roofing granules into athermoplastic-rubber roofing membrane according to an embodiment of theinvention.

FIG. 6 illustrates a method for pressing roofing granules into a roofingmembrane according to an embodiment of the invention.

FIG. 7 illustrates a method for determining a contact angle for pressingroofing granules into a roofing membrane according to an embodiment ofthe invention.

In the appended figures, similar components and/or features may have thesame numerical reference label. Further, various components of the sametype may be distinguished by following the reference label by a letterthat distinguishes among the similar components and/or features. If onlythe first numerical reference label is used in the specification, thedescription is applicable to any one of the similar components and/orfeatures having the same first numerical reference label irrespective ofthe letter suffix.

DETAILED DESCRIPTION OF THE INVENTION

The ensuing description provides exemplary embodiments only, and is notintended to limit the scope, applicability or configuration of thedisclosure. Rather, the ensuing description of the exemplary embodimentswill provide those skilled in the art with an enabling description forimplementing one or more exemplary embodiments. It being understood thatvarious changes may be made in the function and arrangement of elementswithout departing from the spirit and scope of the invention as setforth in the appended claims.

The description here refers generally to viscoelastic roofing materials,which may include SBS Modified Bitumen Roofing Membranes, polymermodified asphalt, rubber modified asphalt, thermoplastic rubbers,modified thermoplastic rubbers, and the like. These materials are oftencap sheets that include a combination of asphalt, polymer, and one ormore fillers. The materials are typically applied atop a roofing systemto protect underlying layers from rain, sun exposure, foot traffic, andthe like. These roofing materials may include any material that exhibitsboth plastic and elastic behaviors and are not necessarily limited toone type. For example, these materials may exhibit plastic behavior atelevated temperatures and elastic behavior at lower temperatures. Sincethese materials may exhibit behaviors, the methods and procedures formanufacturing or working with these materials may need to be slightlyadjusted compared with conventional processes. As described herein, onemanufacturing process that may be more difficult due to the uniqueproperties of these materials is applying granules to a surface of themembranes.

Embodiments of the invention describe methods and apparatus, whichimprove granule adhesion in such roofing materials. In particular, theembodiments described herein improve granule adhesion in viscoelasticmaterial roofing membranes, such as SBS Modified Bitumen RoofingMembranes, thermoplastic rubbers, modified thermoplastic rubbers,polymer modified asphalt, rubber modified asphalt, and the like(hereinafter viscoelastic roofing membranes or granulated modbitmembrane). As described herein, these materials are typicallycharacterized by having properties similar to both plastics and rubbers.For example, these materials may exhibit elastic properties whensubjected to instant forces and exhibit plastic properties when theforces are more delayed. The materials behavior may depend on thetemperature of the material. For example, the material may flow andexhibit plastic behavior typical of polymers at higher temperatures andexhibit elastic behavior typical of rubbers at lower temperatures.

An example of a well-known viscoelastic material is commonly known asSilly Putty®. If silly putty is subjected to an instant stress or force,like being thrown against the ground, the material will bounce orelastically rebound. On the other hand, if the material is subjected toa relatively long stress or force, such as leaving the material on aflat table, the material will flow and puddle. In this manner, thematerial is not a traditional solid or liquid, but exhibits behaviors ofboth depending on the stress or force applied.

Like many roofing membranes, it may be desirable to apply roofinggranules to a surface of viscoelastic roofing membranes by pressing thegranules into a surface of the membranes. The granules are typicallyapplied for aesthetics and/or functional purposes, such as to provideultraviolet (UV) protection and foot traffic protection for the asphaltand underlying membrane. For example, the asphalt may decay with UVexposure and may also decay with foot traffic. The granules protect theunderlayment from such decay or delay the decaying process. Conventionalgranule application processes typical involve applying asphalt to aviscoelastic material mat and applying or dropping granules atop theasphalt and mat. The mat, asphalt, and granules are then passed througha pair of press rollers, which are typically small in diameter and applya single point pressure on the material to mechanically force thegranules into the roofing membrane. Adjustments to conventional pressingoperations include increasing or decreasing a line speed of theoperation, or adjusting the point pressure applied by the pair of pressrollers. This conventional process works well for materials that exhibitplastic behavior, such as APP modified bitumen and oxidized asphaltroofing membranes, because these materials readily deform as thegranules are pressed into the materials.

A particular problem with applying roofing granules to viscoelasticroofing membranes, however, is that these materials exhibit elasticbehavior characteristic similar to rubber materials as the roofingmembrane cools. The elastic behavior causes the roofing membrane todeflect under the instant point load applied by the press rollers duringthe granule adhesion process. The roofing membrane may then rebound orelastically return to position and force the granule out of a temporarypocket created by the point load. As such, a significant portion of thegranules may not properly adhere to the roofing membrane and mayinstantly fall off, or quickly fall off as minor loads are applied tothe granules, such as by an object brushing past the granules.

One method in which the elastic behavior of the viscoelastic materialmay be accounted for is by raising the temperature of the material priorto extrusion of the material. A potential problem with raising thematerial's temperature, however, is that the increased temperature maylead to cross-linking the polymers. Additionally, at elevatedtemperatures, the viscoelastic membrane may exhibit increased plasticbehavior. In these instances, the viscoelastic material may be too soft,which causes the material to surround the granule and encapsulate thegranules as the granules are pressed into the material. This may lead toproblems such as stick ups or bleed through of the asphalt.

In some embodiments, the temperature of the viscoelastic material mayvary due to variations in the environmental temperature, the temperatureof the material during manufacturing, the speed of extrusion of thematerial, and the like. Due to these variations, the temperature of theviscoelastic membrane during the granule pressing operation may vary,which may result in the membrane varying between elastic and plasticbehaviors during the granule pressing operation. Accordingly, a granulepressing operation that is designed for a given behavior of the membrane(i.e., either plastic or elastic) may inadequately press the granules asthe behavior of the membrane varies. For example, if the granulepressing operation is designed based on a plastic response of theviscoelastic membrane, the granules may not be adequately pressed intothe membrane when the membrane exhibits elastic behaviors, and viceversa.

The embodiments described herein optimize the granule adhesion inviscoelastic roofing materials by adjusting the granule pressing timeand/or heat of the roofing materials. For example, the amount of timethe granules are pressed into the membrane may be adjusted based on thetemperature of the viscoelastic roofing material so as to compensate forwhether the material is exhibiting predominantly elastic or plasticbehavior. In one embodiment, the methods and systems described hereinare especially advantageous in pressing granules into materialsexhibiting an elastic behavior. In such embodiments, granule adhesion isimproved by pressing the granules in a manner that relaxes the materialand allows the material to flow around the pressed granules. Forexample, the “dwell time” of the granule pressing operation, or in otherwords an amount of time the granules are pressed into the viscoelasticmaterial, may be increased so that the viscoelastic material is able torelax and flow around the granules in a more plastic manner. Stateddifferently, in one embodiment, the pressure applied to the granules ismore evenly applied and applied over a longer duration to allow thematerial to relax some of the stress and flow around the granule, whichresults in increased granule adhesion.

Applying the granule pressure in this manner also allows theviscoelastic material to flow around the granules and create a goodseal. Creating a good seal encapsulates the bottom of the granule, whichprevents water from flowing between the material and granule and erodingthe glass in the granules, which otherwise results in poor granuleadhesion.

The embodiments described herein also allow the granule pressingoperation to be varied based on the temperature of the viscoelasticmaterial so as to account for an increased elastic or plastic behaviorof the material. For example, the “dwell time” of the granule pressingoperation may be extended or lengthened when the viscoelastic materialis cooler to account for a likely increase in elastic behavior of thematerial. Likewise, the dwell time of the granule pressing operation maybe shortened when the viscoelastic material is warmer to account for alikely increase in plastic behavior of the material. In this manner, thegranule pressing operation may be optimized based on the viscoelasticmaterial's temperature so that the stick up, bleed through, and elasticrebound issues as described herein are minimized.

The embodiments described herein further allow the granule pressingoperation to be varied based on the specific properties of theviscoelastic material so as to account for a measured or determinedelastic or plastic behavior of the material. For example, the “dwelltime” of the granule pressing operation may be extended or shortenedbased on the measured or determined plastic or elastic behavior of thematerial. If the material is measured or determined to exhibit moreplastic behavior, the dwell time may be shortened to minimized bleedthrough and stick up issues. If the material is measured or determinedto exhibit more elastic behavior, the dwell time may be lengthened tominimize elastic rebound issue and properly adhere the granules to theviscoelastic material. Having described embodiments of the inventiongenerally, additional features will be more evident with references tothe figures described below.

Referring now to FIG. 1, illustrated is a graph showing a measuredpressure applied during a granule pressing operation. The dashed linelabeled 1 shows the pressure applied during a conventional pressingoperation using press rollers that apply a single point load. As shownby line 1, the pressure applied to the roofing material is essentiallyzero until the press rollers are encountered. As the material andgranules pass through the press rollers, a relatively high and instantforce is applied. As can be readily understood, when such a pressure isapplied to a membrane that exhibits an elastic response, the membraneabsorbs the pressure, such as by creating a pocket in which the granulessits, and rebounds to force the granule out of the pocket.

The solid line labeled 2 shows the pressure applied during a pressingoperation according to embodiments of the invention. As shown by line 2,the pressure applied to the roofing material is applied in a relativelyeven manner and over a significantly longer duration compared with thepressing operation of line 1. The maximum pressure amplitude applied mayalso be below the pressure applied during the pressing operation of line1, although the pressure amplitude may be varied to be at or near thepressure of line 1 depending on the specifics of the pressing operationand/or viscoelastic material properties. Similarly, the duration of thepressure application may be varied based on the temperature or othercharacteristics of the viscoelastic material as described herein.

Referring now to FIG. 2, illustrated is a graph 200 showing a dynamicmechanical analysis (DMA) frequency-temperature response of astyrene-butadiene-styrene (SBS) modified bitumen roofing membrane.Specifically, graph 200 shows the materials resistance to deformation asa result of temperature and pressure application duration. The pressureapplication duration is shown as an angular frequency (rad/sec) orangular velocity, which corresponds to the speed at which a pressureapplication wheel is turned. Lower angular frequency values correspondto slower speeds for the pressure application wheel. Higher angularfrequencies (e.g., those illustrated on the far right of graph 200) maycorrespond to single pressure point processes while lower angularfrequencies (e.g., those illustrated on the left side of graph 200)correspond to the extended pressure application processes describedherein. The resistance to permanent deformation may be considered as amodulus of the material that takes into account any phase lag times,with higher values representing an increased resistance to permanentdeformation. The phase lag in some material may be about 0 and 45degrees from the applied pressure.

Graph 200 includes 4 plots 10-16. The plots are for a singleviscoelastic material at roughly 4 different temperatures. Specifically,line 10 is for a viscoelastic material at roughly 90° Celsius, line 12is for the viscoelastic material at roughly 80° C., line 14 is for theviscoelastic material at roughly 70° C., and line 16 is for theviscoelastic material at roughly 60° C. As seen in graph 200 as thematerial cools from roughly 90° C. to 60° C., the resistance todeformation increases at any particular angular frequency. This is dueto the material exhibiting a more solid or elastic behavior where thematerial rebounds to some degree from an applied pressure.

As also shown in graph 200 as the angular frequency decreases (i.e., asthe pressure application wheel speed is decreased), the resistance topermanent deformation also decreases. This is due to the viscoelasticmaterial exhibiting a more viscous behavior where the material relaxesand flows in response to the applied pressure. Stated differently, asthe dwell time of the pressure application process is increased, thematerial is more prone to plastic deformation and the amount of“pushback” or rebound exhibited by the viscoelastic material isdecreased. The extended dwell time of the pressure application processeffectively drives granules into the viscoelastic roofing material.

As can be readily understood with reference to graph 200, the ideal“processing window” for a granule adhesion pressing operation is onethat occurs at higher temperatures and/or at lower frequencies, wherethe viscoelastic roofing membrane will exert or exhibit less resistanceto the press rollers. As graph 200 also shows, at lower angularfrequencies the roofing membrane's behavior is less dependent on themembrane's temperature. Stated differently, at lower angularfrequencies, the membrane tends to act more uniformly even at differenttemperatures. As a result, the granule adhesion sensitivity to membranetemperature and viscosity variations is reduced at lower angularfrequencies. Stated differently, at lower angular frequencies, thegranule pressing operation is more uniform and less prone to temperatureand viscosity variations. As such, embodiments of the inventiondescribed herein generally describe granule pressing operation where theangular frequency is relatively low.

The circled range 18 on graph 200 illustrates a range of angularfrequencies where the resistance to permanent deformation is sufficientlow so as to allow adequate adhesion of roofing granules withviscoelastic materials. The range includes angular frequencies of about10 rad/sec and less. At this angular frequency (i.e., 10 rad/sec),resistance to deformation is typically low enough so that the granulepressing operation results in effective granule adhesion. As shown inthe graph, the 10 rad/sec is more effective for higher temperatureviscoelastic membranes (i.e., 90° C.) and much less effective for lowertemperature membranes (i.e., 60° C.). In one embodiment, the angularfrequency may range from about 0.010 to 3 rad/sec or from about 0.10 to2 rad/sec. In a specific embodiment, the angular frequency may rangefrom about 1.0 to 2.0 rad/sec. In these lower angular frequency ranges,the viscoelastic membrane's temperature affects the resistance todeformation less and thus, affects the granule adhesion process less.

To achieve the desired angular frequency, the contact angle (θ) betweenthe viscoelastic membrane and the press roller may be increased, whichresults in an increase in the granule press dwell time. This in turndecreases the frequency (ω) of the granule press pressure signal asdescribed with reference to FIG. 3. The contact angle (θ) may beadjusted to optimize the frequency (ω) of the granule press signalfrequency for a particular line speed (ν). The below equation describesthe parameters of the granule press pressure signal and its relation tothe line speed (ν).

$\theta = \frac{2\;\pi\; v}{r\;\omega}$

In the above equation, (θ) is the contact angle of the granulated modbitmembrane with the press roller, (r) is the radius of the press roller,(ν) is the line speed and (ω) is the angular frequency of the granulepress pressure signal (it is inversely proportional to the granule pressdwell time). As shown in FIG. 1, conventional granule press operationsproduce sharp high frequency (ω) pressure signals at the granule pressrollers. The frequency of this pressure signal is directly proportionalto the line speed (ν). The amplitude is controlled by the force exertedby the pressure rollers. In contrast, the frequency (ω) of the granulepress pressure signal generated by the embodiments described herein istunable by means of the contact angle (θ) and can be made independent ofthe line speed (ν) as shown in the above equation. The amplitude of thepressure signal can be controlled by adjusting the line tension on themembrane.

In some embodiments, the press roller radius (r) will be constant andbased on the specific design of the pressing operation. The frequency(ω) may be selected at an optimum point based on the viscoelasticproperties of the polymer modified coating. The frequency (ω) willtypically fall within the above described ranges, although valuesoutside of this range are possible, and may be based on the membranesfrequency response at varying temperatures as measured by dynamicmechanical analysis (DMA). The required contact angle (θ) may then becalculated based on the desired frequency (ω) and line speed (ν).

For example, considering graph 200 required contact angle (θ) may becalculated based on a desired or optimal granule press frequency (ω).Assuming that the granule press roller used in the operation has adiameter of about 0.5 m and provided an optimal or desired granule pressfrequency (ω) of approximately 2 rad/sec, the required contact angle (θ)may be calculated as a function of line speed (ν) using the aboveequation. The results for various process line speeds are summarized inTable 1.

TABLE 1 Calculation of contact angle (θ) for various line speeds (ν).Line speed ν(m/hr.) 1400 1600 1800 2000 Granule press ω (rad./s) 2.002.00 2.00 2.00 pressure signal Granule press roll r(m) 0.50 0.50 0.500.50 diameter Contact angle θ (rad.) 0.78 π 0.89 π π 1.11 π

Table 1 shows that if the line speed (ν) increases, the contact angle(θ) needs to be increased in order to maintain a constant frequency (ω)of the granule press pressure signal and granule press dwell time foroptimal granule embedment. The amplitude of the pressure signal can beadjusted by adjusting the tension on the membrane, which may be used tocontrol asphalt bleed through.

One advantage among many of decoupling the frequency (ω) and amplitudeof the granule press pressure signal from the line speed (ν) asdescribed above is improvement of granule adhesion and increase processrobustness by lowering granule adhesion sensitivities to line speed,temperature and formulation variations. Another advantage is thetenability of the granule press process to specific operations,viscoelastic membranes, and the like.

Referring now to FIG. 3, illustrated is a granule processing system 300that is designed to press granules into viscoelastic membranes 302 wherethe dwell time of the granule pressure application process is increasedas described herein. System 300 achieves this increased dwell time byincreasing the duration or amount of time that the membrane 302 andgranules are in contact with a pressure wheel 304. In contrast toconventional process that provide high amplitude and short durationpressure curves as shown in FIG. 1, the increased duration of contactwith the pressure wheel 304 ensures that a relatively even pressure isapplied to the granules for a sufficient duration to drive the granulesinto the membrane 304. The pressure wheel 304 is also typically largerin diameter than conventional pressing wheels thereby increasing thecontact duration compared with conventional wheel.

System 300 also includes an adjustable position roller 306 that allowsthe angle of contact, and thus the contact duration, to be adjusted. Forexample, roller 306 may be vertically adjusted relative to press roller304 between a maximum top height that produces an angle of contact θ₁between the membrane 302, granules, and press roller 304, and a maximumbottom height that produces an angle of contact θ₁+θ₂ between themembrane 302, granules, and press roller 304. The increase in the angelof contact θ₂ allows system 300 to be fine-tuned based on the propertiesof the membrane (e.g., temperature, viscoelasticity, amount of polymersor fillers, and the like), based on the line speed, based on a measureor desired frequency (ω), based on the tension in membrane 302, and thelike. Thus, even when granules are being pressed into two membraneshaving similar properties, roller 306 may be adjusted to fine tune thepressing process and account for small variations, such as variations intemperature or line speed. The resulting membranes may be relativelyuniform in granule adhesion characteristics despite the small variationsin the granule pressing process.

A typical operation of system 300 involves dispensing granules atopmembrane 302 prior to the membrane and granules passing over pressroller 304. The granules are commonly dispensed via a hopper 307 that ispositioned along a path of the membrane proximally of press roller 304and distally an extrusion device 305. Press roller 304 presses or drivesthe granules into the asphalt material of membrane 302 in the mannerdescribed herein. Additional material, such as a sand release agent, maybe dispensed onto membrane 302 from one or more hoppers 308. Membrane302 then passes over adjustable roller 306, and optionally one or moreother rollers, en route to a final destination. One or more pressrollers, such as those used in conventional systems, may be used topress the sand or other material into membrane 302 at a downstreamprocess. These other press rollers, however, typically apply singlepoint loads and are thus not as effective as press roller 304 atensuring optimal granule adhesion for the reasons described herein. FIG.4 illustrates granule processing system 300 with the adjustable roller306 positioned in front of press roller 304 so that membrane 302 passesover adjustable roller 306 before contacting press roller 304.

Another advantage of system 300 is that the press roller 304 ispositioned closer than many conventional press rollers to the granuledispensing hopper or device 307 and/or to where the membrane 302 isextruded 305. The membrane 302 is typically extruded at a temperatureabove 100° C. and commonly at a temperature above 150° C. The membrane302 cools as it is routed along the various rollers after extrusion.Positioning press roller 304 closer to where the membrane 302 isextruded ensures that the membrane is likely to be hot when the membranecontacts the press roller, which facilitates in the granule pressingprocess (as shown in FIG. 2) and subsequent granule adhesion. In someembodiments, system 300 may be positioned away from extrusion device 305such that the membrane 302 cools by a considerable or substantial amountbefore contacting press roller 304. An additional advantage of system300 is that the increased dwell time effectively adheres the granuleswith membrane 302 even when the membrane experiences a considerableamount of cooling, which may result in the membrane exhibiting increasedelastic behavior. Conventional point load press rollers are oftenineffective at pressing granules into a membrane when such membranesexperience considerable cooling.

As described above, a contact angle θ may be calculated based on thecharacteristics of the specific system 300 (i.e., the press roller 304radius and the line speed (ν)) and based on a calculated, determined, ordesired frequency (ω). The frequency (ω) may be calculated by using orgenerating a chart, such as that shown in FIG. 2, and determining asufficiently low resistance to deformation for the membrane and anangular frequency that corresponds to that value. In making thisdetermination, a temperature of the membrane may be taken intoconsideration as described herein. If the calculated contact angle θ isgreater than a lowest contact angle value θ₁ of system 300, which is acontact angle produced when roller 306 is vertically adjusted to amaximum height, roller 306 may be adjusted vertically downward toincrease the contact angle θ₁ of system 300. The contact angle of system300 may be adjusted to have any value between the lowest contact anglevalue γ₁ and a maximum contact angle value of θ₁+θ₂. The maximum contactangle value θ₁+θ₂ is essentially only constrained by the adjustabilityof roller 306. The resolution or maximum adjustment angle θ₂ may varywidely, but in one embodiment is between about 60 and 120 degrees,between about 75 and 105 degrees, between about 85 and 95 degrees, andis commonly about 90 degrees. The fine resolution of the contact angleadjustment allows system 300 to be tailored to essentially any type ofmembrane or pressing operation.

If the calculated contact angle θ is less than the lowest contact anglevalue θ₁ of system 300, the line speed may be increased, the tension inmembrane 302 reduced, or the radius of pressing wheel 304 reduced toincrease the value of the contact angle θ to be about equal to orgreater than θ₁. In some embodiments, a contact angle θ of less than θ₁does not require any changes to the granule processing operation.

In some embodiments, the temperature of the membrane 302 may becontrolled to facilitate in the granule pressing operation. For example,if the temperature of the membrane 302 is too cold so that the membraneis exhibiting elastic behavior, the membrane may be heated to raise thetemperature so that the membrane exhibits less elastic behavior and/orincrease plastic behavior. The membrane may be heated by raising thetemperature of the material prior to extrusion and/or positioning one ormore heaters, such as lights, that heat the membrane prior to pressrolling. In another embodiment, variations in temperature may beaccounted for by selecting a lower frequency (ω) where the pressingoperation is likely less affected by temperature variations.

While the dwell time typically depends on the properties of the membraneand the granule pressing operation, in one embodiment, the dwell time isbetween about 0.01 and 1.0 millisecond, between about 0.05 and 0.05millisecond, or about 0.01 milliseconds. These value are exemplary only,however, and other values (shorter or longer durations) may be useddepending on the specific materials and processing conditions. In oneembodiment, press roller 304 may apply a pressure between about X and Yto press the granules into membrane 302. This pressure may be appliedover a contact angle of at least 90 degrees, and more commonly over 120degrees. When roller 306 is adjusted to increase the contact angle θ byup to the additional contact angle θ₂, this pressure may be applied overa contact angle of up to 180 or 210 degrees or more. In this manner, thesingle point load problem with conventional granule pressing processesis eliminated or greatly reduced. This configuration also allows theline speed to be increased without negatively affecting the granulepressing operation since the contact angle θ make be increased toaccount for the increased line speed. In this manner, the process timemay be increased. The press roller 304 of system 300 is typically largerthan conventional press rollers. In one embodiment, press roller 304 maybe about 0.5 m in diameter, which is considerable larger than the pressrollers of conventional systems, which may be 0.1 m in diameter or less.System 300 is not limited to these dimensions however, and virtually anysized press roller may be used.

Although not shown, in some embodiments, system 300 may include acomputing device (or be communicatively coupled therewith) to calculateone or more of the parameters described above (e.g., θ, ν, r, ω).Further, the computing device (not shown) may be used to implement anyof the methods described herein, or any portion thereof. In someembodiments, the computing device may include one or more processorsthat are communicatively coupled with one or more memory devices, whichmay be internal and/or external to the computing system. The memorydevices may include instructions or code, which cause the one or moreprocessors to perform one or more of the method step operationsdescribed herein. The computing device may also receive input fromand/or provide output to one or more other systems, users, externaldevices, and the like. The computing system may further communicateand/or be linked to one or more networks to route information and/orreceive various input or instructions.

Referring now to FIG. 5, illustrated is a method 500 for pressingroofing granules into a thermoplastic-rubber roofing membrane. At block510 a thermoplastic rubber material may be provided. The thermoplasticrubber material may be similar to any of the material described herein.At block 520, the thermoplastic rubber material may be heated, such asto melt the thermoplastic rubber material. At block 530, the heatedthermoplastic rubber material may be extruded (e.g., via extrusiondevice 305) to form a roofing membrane having a first surface and asecond surface opposite the first surface (hereinafter roofingmembrane). At block 540, roofing granules may be applied atop the firstsurface (e.g., via hopper 307).

At block 550, a contact angle may be calculated that represents aneffective amount of contact between the roofing membrane and a pressroller. In some embodiments, the contact angle may be calculated basedon a line speed of the roofing membrane through a granule pressingsystem or operation. In some embodiments, the contact angle mayadditionally, or alternatively, be calculated based on an angularfrequency of the press roller and/or a radius of the press roller. Asdescribed herein, the angular frequency of the press roller may bedetermined based on a temperature of the roofing membrane. In someembodiments, the angular frequency may be about 10.00 rad/sec or less,or about 1.00 rad/sec or less.

At block 560, the contact between the thermoplastic rubber membrane andthe press roller may be adjusted so as to correspond to the effectiveamount of contact. In some embodiments, adjusting the contact betweenthe thermoplastic rubber membrane and the press roller includesadjusting a position of a second roller (e.g., roller 306) relative tothe press roller (e.g., roller 304). At block 570, the roofing granulesmay be pressed into the first surface of the thermoplastic rubbermembrane via the press roller. In some embodiments, the radius of thepress roller may be between about 0.25 and about 0.75 meters. In otherembodiments, the press roller may be about 0.5 meters.

Referring now to FIG. 6, illustrated is a method 600 for pressingroofing granules into a roofing membrane. At block 610, a roofingmembrane is provided. The roofing membrane may be similar to any of themembranes described herein. At block 620, roofing granules are appliedatop a surface of the roofing membrane. At block 630, a position of asecond roller is adjusted relative to a first roller so as to vary anamount of contact between the roofing membrane and the first roller. Atblock 640, the roofing granules are pressed into the roofing membranevia the first roller.

In some embodiments, method 600 may also include the steps of:determining a line speed of the roofing membrane through a granule presssystem, calculating a contact value based on the line speed of theroofing membrane, where the contact value represents an effective amountof contact between the roofing membrane and the first roller, andadjusting the position of the second roller so that the amount ofcontact between the roofing membrane and the first roller corresponds tothe effective amount of contact. In some embodiments, method 600 mayfurther include: determining an angular frequency of the first rollerand calculating the contact value based additionally on the angularfrequency of the first roller.

Referring now to FIG. 7, illustrated is a method 700 for determining acontact angle for pressing roofing granules into a roofing membrane. Atblock 710, a radius of a press roller is determined. As describedherein, the press roller is used to press roofing granules into theroofing membrane. At block 720, an angular frequency of the press rolleris determined. At block 730, a line speed of the roofing membranethrough a granule pressing system is determined. At block 740, thecontact angle is calculated based on the radius of the press roller, theangular frequency of the press roller, and/or the line speed of theroofing membrane. As described herein, the contact angle defines orrepresents an amount of contact the roofing membrane should have withthe press roller to effectively press the granules into the roofingmembrane. In some embodiments, the angular frequency of the press rollermay be determined based on the temperature of the roofing membrane.

EXAMPLES

Referring to Table 2 below, provided is data from an experiment thatshows that increasing the temperature and/or increasing the granulepress dwell time (i.e. decreasing the frequency (ω) of the granule presspressure signal) result in significant improvements to granule adhesionper ASTM D 4977-89. The improvement in granule adhesion was measuredbased on a reduction in granule loss with most test samples exhibiting a90% or more reduction in granule loss compared to a control sample. Theexperiment was conducted by re-pressing the granules of typical SBSmembrane in a lab setting. The experiment shows the viability ofincreasing the granule press dwell time (i.e. decreasing the frequency(ω) of the granule press pressure signal).

TABLE 2 Results of a granule adhesion experiment Granule GranuleRe-Pressing Re-Pressing Loss (g)- Reduction Temperature Dwell Time ASTMD in granule (° C.) ^(a) (min) ^(a) 4977-89 ^(b) loss (%) None- controlNone- control 0.9 ± 0.3 — sample sample 120 5 — Asphalt bleed through120 + spacer 5 0.09 90 115 5 0.10 89 115 10 0.05 94 110 10 0.11 88 11015 0.26 71

All the samples were roughly 10 inch by 10 inch specimen. The controlsample, which was not heated or re-pressed, exhibited a granule loss ofapproximately 0.9±0.3. At a temperature of approximately 120° C. andwith a re-pressing dwell time of approximately 5 minutes, the first testsample exhibited asphalt bleed through, which indicates that themembrane material was too soft and/or the pressing operation too long. Asecond test sample was run under the approximate same conditions with aspacer that limited the pressure applied during the re-pressing processand a granule loss of approximately 0.09 was measured, which correspondsto approximately a 90% reduction in granule loss. A third test samplewas heated to approximately 115° C. and a re-pressing dwell time ofapproximately 5 minutes was used, which resulted in a granule loss ofapproximately 0.10 corresponding to an approximately 89% reduction ingranule loss. A fourth test sample was heated to approximately 115° C.and a re-pressing dwell time of approximately 10 minutes was used, whichresulted in a granule loss of approximately 0.05 corresponding to anapproximately 94% reduction in granule loss. A fifth and sixth samplewere heated to approximately 110° C. and a re-pressing dwell time ofrespectively 10 and 15 minutes were used, which resulted in respectivegranule losses of 0.11 and 0.26, or respectively 88% and 71% reductionin granule loss. A spacer was not used for test samples three throughsix. These results show that significant reductions in granule loss arepossible by increasing the dwell time and/or temperature of the granulepressing operation.

While the embodiments described herein typically refer to the processbeing applied to viscoelastic materials, such as SBS Modified BitumenRoofing Membranes, polymer modified asphalt, rubber modified asphalt,thermoplastic rubbers, modified thermoplastic rubbers, and the like, theprocess is not limited to these materials. For example, the increaseddwell time and press roller concepts described herein may be applied toconventional membranes in a granule pressing process in order to speedup these processes. For example, the dwell time of the pressingoperation may be increased as described herein so that the line speedmay be increased while the pressure applied to the membrane is keptrelatively the same. Accordingly, the concepts described herein may beapplied to essentially any granule pressing operation.

Having described several embodiments, it will be recognized by those ofskill in the art that various modifications, alternative constructions,and equivalents may be used without departing from the spirit of theinvention. Additionally, a number of well-known processes and elementshave not been described in order to avoid unnecessarily obscuring thepresent invention. Accordingly, the above description should not betaken as limiting the scope of the invention.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimits of that range is also specifically disclosed. Each smaller rangebetween any stated value or intervening value in a stated range and anyother stated or intervening value in that stated range is encompassed.The upper and lower limits of these smaller ranges may independently beincluded or excluded in the range, and each range where either, neitheror both limits are included in the smaller ranges is also encompassedwithin the invention, subject to any specifically excluded limit in thestated range. Where the stated range includes one or both of the limits,ranges excluding either or both of those included limits are alsoincluded.

As used herein and in the appended claims, the singular forms “a”, “an”,and “the” include plural referents unless the context clearly dictatesotherwise. Thus, for example, reference to “a process” includes aplurality of such processes and reference to “the device” includesreference to one or more devices and equivalents thereof known to thoseskilled in the art, and so forth.

Also, the words “comprise,” “comprising,” “include,” “including,” and“includes” when used in this specification and in the following claimsare intended to specify the presence of stated features, integers,components, or steps, but they do not preclude the presence or additionof one or more other features, integers, components, steps, acts, orgroups.

What is claimed is:
 1. A system for pressing granules into a roofingmembrane comprising: a granule application device positionable above atop surface of a roofing membrane and configured to dispense roofinggranules onto the top surface of the roofing membrane as the roofingmembrane passes underneath the granule application device; a firstroller positioned along a path of the roofing membrane, the first rollerbeing configured to press the roofing granules into the roofingmembrane; and a second roller positioned along the path of the roofingmembrane and adjacent the first roller, the second roller beingadjustable relative to the first roller to vary an angle of contactbetween the roofing membrane and the first roller and to vary an amountof time that the roofing granules are pressed into the roofing membrane,the angle of contact being calculated based on a line speed of theroofing membrane.
 2. The system of claim 1, wherein the second roller ispositioned immediately adjacent the first roller along the path.
 3. Thesystem of claim 1, wherein the second roller is linearly adjustablerelative to the first roller.
 4. The system of claim 1, whereinadjustment of the second roller wraps the roofing membrane around atleast a portion of the first roller or unwraps the roofing membranetherefrom.
 5. The system of claim 1, wherein the first roller comprisesa radius of between about 0.25 and 0.75 meters.
 6. The system of claim5, wherein the first roller comprises a radius of about 0.5 meters. 7.The system of claim 1, wherein the second roller is configured to varythe amount of contact between the roofing membrane and the first rollerby between about 60 and 120 degrees (between 1.04 and 2.09 radians). 8.The system of claim 7, wherein the second roller is configured to varythe amount of contact between the roofing membrane and the first rollerby between about 75 and 105 degrees (between 1.30 and 1.83 radians). 9.The system of claim 8, wherein the second roller is configured to varythe amount of contact between the roofing membrane and the first rollerby between about 85 and 95 degrees (between 1.48 and 1.66 radians).